For leak testing closed containers which are at least partially filled with a liquid product it is known from e.g. U.S. Pat. No. 5,907,093 of the same applicant as the applicant of the present application to expose respective containers to be leak tested to an external pressure which is at least as low as vapor pressure of a component of the liquid content in the container. This technique exploits the fact that liquid which is suctioned out through a leak in the container, evaporates resulting in a substantial increase of the pressure outside the container. Thereby, for such leak testing, the container under test is kept integral. Nevertheless, the addressed highly accurate testing method is limited to testing containers which are filled with a liquid product.
Leak testing methods and accordingly methods for manufacturing closed and filled containers which are unleaky and which are operated without harming integrity of the containers are of high interest e.g. for inline testing thereby determining which containers fulfill unleakiness conditions and which do not.
It is an object of the present invention to provide for a testing method, a manufacturing method and a respective apparatus as addressed above which are applicable to closed and filled containers irrespective whether the filling product is a solid, e.g. powderous, liquid or even gaseous. The only limiting factor is that the containers which are subjected to testing should at least partially be filled with a gas. Thereby, it should be considered that prefilled closed containers practically always have some percentage of their internal volume containing gas.
According to the present invention the method for leak testing closed, at least partially gas filled containers comprises                subjecting a closed, at least partially gas filled container to an atmosphere of test gas at a pressure which is larger than pressure prevailing within the close, at least partially gas filled container, whereby the test gas comprises at least one gas species;        sensing after an amount of time the closed, partially gas filled container has been subjected to the atmosphere of test gas at the addressed pressure, the amount of at least the addressed gas species of the test gas within the closed, at least partially gas filled container as a leak indication.        
Thus, an addressed container to be tested is subjected to an external pressure which is higher than the pressure prevailing within the container to be tested. This leads to gas or at least a gas species of the test gas to penetrate into the container to be tested which is on lower pressure. Sensing the amount of such gas species within the container which is kept integral and closed is exploited as a leak indication. The amount of gas which penetrates into the container is dependent of a leak being present or not, and if a leak is present, of the extent of such leak. By appropriately selecting the amount of time during which such container to be tested is subjected to the external overpressure of test gas and/or by appropriately selecting the amount of such overpressure and/or possibly also by selecting the gas species which are contained in the test gas, it becomes possible to detect extremely small leaks in the container, down to 1 μm diameter and less.
In one embodiment of the method according to the present invention, which may be combined with any of the subsequently addressed embodiments, a wall of the closed and at least partially gas filled container to be tested is selected to be transparent to light of a laser. The sensing thereby comprises subjecting the gas in the closed and at least partially gas filled container to the light of the beam of the laser, which beam being applied onto the addressed wall. The amount of gas species in the container is sensed from such light being transmitted through and/or being reflected from the closed and at least partially gas filled container.
Thereby, the selective absorption of light by the gas species in the container is exploited, e.g. according to a technique which is known from the U.S. Pat. No. 7,222,537 of the same applicant as the present application.
Although other techniques may be applied to sense or monitor whether during the time the container to be tested is exposed to the test gas atmosphere at the addressed high pressure, how much gas has penetrated into the container as e.g. a weighing technique etc the addressed laser technique has revealed to be highly suited as fast, accurate and relatively inexpensive.
In one embodiment of the method according to the present invention which may be combined with any embodiment addressed to now and subsequently addressed, the species in the test gas, is nominally not comprised in the gas within the closed, at least partially gas filled container. Thus, as an example, frequently the content of closed and filled containers should not come in contact with oxygen. This is e.g. the case for vials or syringes which contain medical substances.
In such a case, the test gas may comprise the addressed species—oxygen—and sensing comprises in fact monitoring in the container under test, whether such a gas species—oxygen—is present or not within the container after having been exposed to the pressurized test gas atmosphere with such species.
If on the other hand the container to be tested nominally does contain the gas species, the amount of which being sensed in the container and after its exposure to the test gas atmosphere with the addressed species and at the addressed elevated pressure, then sensing for the leak indication may comprise monitoring a difference or an increase of the amount of such gas species in the addressed container due to exposure to the test gas atmosphere.
In a further embodiment of the present invention, which may be combined with any of the formerly addressed embodiments as well as with any of the subsequently addressed embodiments, sensing comprises sensing at a first point of time and at least at a second deferred point of time and forming a difference of the amounts sensed at the addressed two or more points in time.
This embodiment is especially suited in the addressed case where the gas species to be sensed is nominally present in the container, but may also be applied in that case where nominally such gas species—e.g. oxygen—is not present in the container under test.
In one embodiment of the method according to the present invention which may be combined with any of the already addressed embodiments as well as with any of the subsequently addressed embodiments, the addressed sensing comprises sensing of the amount of gas species in the container while the container is subjected to the test gas atmosphere under the addressed pressure.
This e.g. allows terminating a testing cycle as soon as the addressed sensing reveals leakiness of the container.
In a further embodiment, which may be combined with any of the formerly addressed embodiments as well as with the embodiments to be subsequently addressed, the test gas comprises oxygen, is preferably air or oxygen enriched air.
In a further embodiment, which may be combined with any of the preaddressed embodiments as well as with any of the embodiments to be subsequently addressed, the closed, at least partially gas filled container to be tested is subjected to the test gas atmosphere at the addressed pressure during a predetermined amount of time.
By this embodiment it becomes possible to perform pressurizing of the container or of containers by the addressed test atmosphere remote from performing the addressed sensing. As will be subsequently addressed, this has e.g. the advantage that a batch of containers to be tested may be simultaneously subjected to the test gas atmosphere at the addressed pressure. Thereby, e.g. for in inline testing a stream of containers by the technique according to the invention feed through may substantially be increased, especially if additionally parallel batch processing is exploited.
It has further to be pointed out that sensing while the containers are subjected to the test gas atmosphere may be advantageously combined with a sensing after a predetermined amount of time in that such predetermined amount of time establishes for a time limit up to which sensing is performed, while the container or the containers are exposed to the test gas atmosphere. If after such predetermined amount of time sensing establishes that the monitored amount of gas species does not suffice to establish the container to be leaky, testing is ended and the respective container is considered unleaky.
In a further embodiment, which may be combined with any of the formerly addressed embodiments as well as with any of the subsequently addressed embodiments, a multitude of closed, at least partially gas filled containers—a batch of containers—is simultaneously subjected to the test gas atmosphere at the addressed overpressure.
Thereby and in a further embodiment the containers of the just addressed batch are exposed to the addressed sensing step, while a further batch of containers is subjected to test gas atmosphere.
Thereby, in one embodiment the addressed sensing is performed subsequently with respect to simultaneously subjecting the multitude of containers—the respective batch—to the test gas atmosphere at the addressed pressure. Such sensing is performed simultaneously upon a number of containers which is smaller than the number of the addressed multitude, that is of the addressed batch.
Such sensing, subsequent to batch subjecting to test gas atmosphere is e.g. performed upon one by one of the addressed containers. This taking into account that the sensing operation is normally much faster than the process step of subjecting the addressed container to the test gas atmosphere, especially if very small leaks are to be detected.
The method for manufacturing closed, at least partially gas filled containers which are unleaky and according to the present invention comprises                providing a closed, at least partially gas filled container,        subjecting this container to a testing method as was addressed above in one of any of its embodiments and establishing the container to be unleaky if the sensed amount is below a predetermined value.        
The present invention is further directed on an apparatus for leak testing closed containers which comprises                a biasing chamber for at least one container to be tested;        a source of pressurized gas which is connected to the biasing chamber and        a sensing arrangement for sensing the amount of a gas species in the closed container whereby the gas species as addressed is at least a part of the pressurised gas.        
In one embodiment of the apparatus which may be combined with any of the preaddressed embodiments of the apparatus according to the invention and with any of the subsequently addressed embodiments, the gas comprises oxygen and in a further embodiment is air or oxygen-enriched air.
In one embodiment of the apparatus according to the present invention, which may be combined with any of the preaddressed embodiments of the apparatus as well as with any of the subsequently addressed embodiments, the sensing arrangement comprises a laser arrangement which generates a laser beam directed upon at least one of the addressed containers within the sensing arrangement.
In a further embodiment of the apparatus according to the invention, which may be combined with any of the preaddressed embodiments, at least a part of the sensing arrangement is operating within the biasing chamber.
In addition or alternatively and according to a further embodiment, at least a part of the sensing arrangement is provided remote from the biasing chamber.
In one embodiment of the apparatus, which may be combined with any of the formerly addressed embodiments or with any of the subsequently addressed embodiments, the biasing chamber is tailored to accommodate a batch of containers.
In one embodiment of the apparatus, which may be combined with any of the formerly addressed embodiments or with any of the subsequently addressed embodiments the apparatus comprises more than one of the biasing chambers.
Thereby and as a further embodiment a number of sensing arrangements is smaller than the number of biasing chambers.
The containers which are leak tested or which are manufactured according to the present invention or which are treated by the apparatus according to the invention are in one embodiment of glass or of a plastic material. They are further containers as e.g. vials or syringe bodies for medical application.